Balanced parametric amplifiers

ABSTRACT

Examples are described of a balanced parametric amplifier employing two loosely-coupled strip conductors, one of which is fed signals via a strip conductor connected at its center. Varactors are connected from each end of the signal-side strip to a ground plane, which completes the idler circuit. The pump standing wave is adjusted to place a null at the signal point and to apply equal amplitude, opposite-phase pump voltages to the varactors.

United States Patent [72] Inventor PII-II Chm-my 3,111,628 11/1963 Landauer 330/4.5 Providence, 8.1. 3,146,403 8/1964 Bobisch et al. 330/4.6 [2]] App]. No. 810,295 3,175,164 3/1965 Schreiner 330/49 [22] Filed Mar. 25,1969 3,218,564 11/1965 Seidel 330/49 [45] Patented July 27,1971 3,219,941 11/1965 Engelbrecht 330/49 [73] Assignee MlcmwlveAmociltes, Inc. 3,320,542 5/1967 Hsu et a1 330/4.6 Burlington, M885. 3,391 ,346 7/1968 Uh1ir 330/4.9

Primary ExaminerRoy Lake 54] BALANCED PARAMETRIC AMPLIFIERS Assistant Examiner-Darwin R. Hostetter 8 Claims, 4 Drawing Figs. Artorney Rosen and Steinhilper {52] US. Cl 330/43,

330/56 ABSTRACT: Examples are described of a balanced paramet- {51] Int. Cl 110317/04 ric amplifier employing two loosely-coupled strip conductors, [50] Field of Search 330/4-9, one of which is fed signals via a strip conductor connected at its center. Varactors are connected from each end of the signal-side strip to a ground plane, which completes the idler 1 1 Refer!!! cued circuit. The pump standing wave is adjusted to place a null at UNITED STATES PATENTS the signal point and to apply equal amplitude, opposite-phase 3,016,492 1/1962 Landauer 330/45 pump voltages t t e a acto s.

PATENTEU JUL27 I971 INPUT SIGNAL QUARTER- CIRCU LATOR AMPLIFIER OUTPUT WAVE TRANSFORMER SHEET 1 [IF 4 PUMP CIRCUIT d TAPERED IIIXEBIE C8 Cd FILTER) 0 II PUMP L INPUT s F POWER s d L Rd moves (2) a IDLER cmculT SIGNAL CIRCUIT SIGNAL-FREQUENCY TUNING INDUCTANCE DIODE INDUCTANCE C JUNCTION CAPACITANCE C STRAY CAPACITANCE R SERIES RESISTANCE FIG. I

PRI QR ART INVENTOR PAUL CHORNEY BY $05 4/! S'IZ'M/HILFA'K ATTORNEYS PATENTEUJuL27|9n 3,596,197

sum 2 or 4 (b) COUPLED LINES WITH LOADING FIG. 2

INVENTOR PAUL CHORNEY BY $055M 8 SrnA/mLpnQ ATTORNEY S PATENTEDJULZ'IIB?! 3,596,197

sum 3 or 4 INPUT S|GNAL'\ 34 OUTPUT SIGNAL PuMP- 4 FIG. 3

INVENTOR PAUL CHORNEY BY 7P0 5 E4 8 STFMAIL 4 51i AT TO RNEY S BALANCED PARAMETRIC AMPLIFIERS BACKGROUND OF THE INVENTION It is known to decouple the pump. signal and idler circuits in a parametric amplifier with a balanced scheme involving a pair of voltage-variable semiconductor diodes, sometimes called varactors." The Final Report, Contract No. DA-36-0 39-SC-87405; Aug. I962, entitled Development of Tunable C-Band Reactance Amplifiers," describes such a scheme as realized in coaxial transmission lines and reduced-height waveguide. FIG. 1 of the accompanying drawings is reproduced directly from that report, and illustrates the prin' ciple of this form ot' balanced amplifier. A pair of such diodes D, and D, (each represented, respectively, by its diode inductance L,,, its junction capacitance C its series resistance R,, and its stay capacitance C are connected with like electrodes to one end of a signal input quarter-wave transformer having a signal-frequency tuning inductance L the equivalent circuit being such that the pair of diodes are connected in parallel to the signal and are pumped effectively by a center-tapped transformer the secondary winding of which is comprised of the two diode inductances L /L in series. Thus, the signal is applied to both diodes in phase with respect to the center tap l 1, whereas the diodes are pumped l80 out of phase with respect to the center tap. The pump frequency cannot couple to the signal circuit, as there is effectively zero voltage applied between the inner and outer conductors of the coaxial line because of the balanced arrangement. Conversely, the signal does not couple to the pump circuit, as there is effectively zero voltage appearing on the pump side 12 of the transformer 10 because of the balanced arrangement. The idler current circulates in the loop (11-14-15) formed by the signal side of the transformer 10 in series with the two diodes. The idler frequency can couple to the pump circuit but not the signal circuit, again because of the symmetries involved. The idler frequency can be kept out of the pump circuit, if desired, by the use of appropriate filters.

This balanced amplifier arrangement is effective in mutually isolating the pump, signal and idler circuits. As the referenced report states, it can be tuned over a band of approximately 7 percent, by altering the diode bias, thus varying the resonant frequency of the idler circuit, without changing the pump frequency.

I have discovered that balanced parametric amplifiers of the kind schematically represented in FIG. 1 can be realized in strip transmission lines, and in integrated circuits, and the like, utilizing the properties of coupled transmission lines.

The properties of coupled transmission lines are treated in the relevant literature; see for example: Oliver, B. M., Directional Electromagnetic Couplers" Proc. IRE Vol. 42, pp. 1686- 1692, Nov. 1954; Knechtli, R. C., Further Analysis of Transmission-Line Directional Couplers" Proc. IRE Vol. 43, pp. 867-869, July 1955', and Jones E. M. T. and Bolljahn, J. T. "Coupled-Strip-Transmission-Line Filters and Directional Couplers Trans. IRE, Vol. MIT-4 pp. 75--8l, Apr. 1956. FIG. 2 (a) of the accompanying drawings schematically represents a pair of coupled transmission lines 21 and 22 located between ground planes 23 and 24. The terminals of line 21 are designated 2" and 3; the terminals of line 22 are designated "1" and "4." As shown in FIG. 2 (b), the lines 21 and 22 are coupled over an electrical length 0." Because this configuration has two center conductors, there are two nonnal TEM modes, one designated even" and the other odd.

If a driving voltage V is applied at terminal 1, when the loads on terminals 2, 3 and 4 are matched to the coupled system(i.e: Z =Z the following relationships exist:

The characteristic impedance of the coupled system is given y k sin 0 1-10 cos 0 DESCRIPTION OF THE INVENTION Some embodiments of the invention are described with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of prior art balanced parametric amplifiers as described above;

FIG. 2 represents a pair of coupled strip transmission lines, as described above;

FIG. 3 schematically illustrates a balanced parametric amplifier according to the invention; and

FIG. 4 schematically illustrates another balanced parametric amplifier according to the invention.

In FIG. 3, a pair of coupled transmission lines 31, 32 of electrically length 0 is center fed by a signal line 33, through a circulator 34. These lines are strip conductors in a parallel-plate system, other components of which (i.e: double or single ground planes) are not shown, being well-known in the art. See Harvey A.F. Microwave Engineering Academic Press, New York, 1963, ch. 9-P arallel Plate Systems. The use of a circulator to introduce and remove a signal as shown in FIG. 3 is also well-known. The coupled line 31 on the signal side is terminated in a varactor diode 35, 36 at each end, 2, 3, respectively. On the pump side 32 of the coupled line, a short circuit 37 (or other appropriate reactance) is located at one end 38 (adjacent terminal 4) so that the null 40 of the voltage standing wave 41 of pump voltage V,, is located at the center 42 of the coupled line section 31, 32. The pump signal is applied at the other end 39 of line 32, adjacent terminal 1. If a short circuit 37 is used, the distance between the center 42 of the coupled lines and the short circuit should be an integral number of half wavelengths, in order that the diodes 35, 36 be pumped at equal amplitudes and out of phase. A pump voltage null is thus provided at the junction with the signal circuit. If also the coupling between the transmission lines is weak (k 1), the pump is decoupled from the signal circuit.

With this arrangement the pump, signal and idler circuits are mutually decoupled. Because of the location of the standing wave 41, the diodes 35, 36 are pumped with equal amplitudes but 180 out of phase. The signal power splits in phase between the two diodes because of the symmetry. The coupled transmission lines with the center feed on the signal side 31 serves the same purpose as the center-tapped transformer L /L shown in FIG. 1. The idler current circulates in the loop fonned by the signal side 31 of the coupled lines, the varactors 35, 36 and a ground plane (represented by the ground symbols 45, 46). The electrical length 0 is adjusted so that the idler'impedance is zero, which is the optimum condition for amplification. The idler does not couple to the signal circuit, but it can couple to the pump circuit.

The coupling between the transmission lines may be weak, and the pump power need not be excessive, since on the pump side 32 of the coupled lines, a resonant section may be set up by introducing appropriate discontinuities.

FIG. 4 illustrates that other forms of the invention are possible. Two parametric amplifiers 51 and 52, each similar to the amplifier of FIG. 3, are coupled to pump signal line 53 via line sections 54, 55, respectively, each coupled section having the same electrical length 0. Each amplifier is centerfed by a signal line 48, 49, respectively. The electrical distance 1 between them, and the electrical distance I from amplifier 52 to the grounded end 57 of the pump line 53 are adjusted so that the voltage standing wave 56 of the pump voltage V, presents a null 58, 59 at the center of the coupled section of each amplifier 51, 52, respectively, and so that the standing wave is located to pump the varactors 61, 62 and 63, 64 of each respective amplifier with equal amplitudes but 180 out of phase. The electrical distance D' which is shown in FIG; 4 is such that corresponding varactors of each amplifier, namely 61 and 63, or 62 and 64, are pumped in like phase.

The hybrid junction 70 divides an input signal at tenninal A into two equal parts and transmits the parts via terminals B and C to the signal lines 48, 49, respectively. Amplified signals from the signal lines recombine in the hybrid junction and emerge from its terminal D as the output signal of the system. The magnitude of b', the electrical distance between the amplifiers 51, 52 can be adjusted to accommodate the properties of the hybrid junction in this respect. As is known, a hybrid junction (or 3db. directional coupler, which has similar properties) can also be realized in a parallel plate system.

From these examples, it will be recognized that the invention can take other forms.

What I claim is:

l. A balanced parametric amplifier comprising first and second transmission lines coupled together over a prescribed electrical length, first applied-energy variable impedance means coupled to a first terminal to one end of the coupled length of said first line, second applied-energy variable impedance means coupled to a second terminal at the other end of the coupled length of said first line, signal means coupled to said first line substantially in the center of its coupled length,

means completing a current loop for idler current through said coupled length and both of said variable impedance means, said second line having an input terminal for pump frequency energy at one end of the coupled length, and means at the other end of the coupled length of said second line to adjust a standing wave of pump voltage to apply pump energy to said variable impedance means with substantially equal amplitudes but substantially out of phase.

2. An amplifier according to claim 1 in which said electrical length is adjusted so that the idler impedance is substantially zero.

3. An amplifier according to claim 1 in which said variable impedance means are varactors having one pair of like electrodes connected respectively to said first and second terminals and the remaining pair of like electrodes connected to a common ground.

4. An amplifier according to claim 3 in which said adjusting means for said second line is an extension of said second line for a prescribed electrical length beyond said coupled section and terminated in said common ground.

5. An amplifier according to claim 1 in which said lines are strip conductors in a parallel-plate system.

6. An amplifier according to claim 3 in which said lines are strip conductors in a parallel plate system, and said common ground is a ground plane of said system.

7. A balanced parametric amplifier system comprising first and second amplifiers each according to claim 1, hybrid junction means having first, second, third and fourth tenninals and the property that a signal introduced via said first terminal is transmitted to said second and third terminals and similar signals introduced at said second and third terminals combine to appear at said fourth terminal, the signal means of said first amplifier being coupled to said second terminal, and the signal means of said second amplifier being coupled to said third terminal. 8. A balanced amplifier system according to claim 7 in which the second transmission lines of said amplifiers are successive segments of a single transmission line for supporting a single pump voltage standing wave for both amplifiers. 

1. A balanced parametric amplifier comprising first and second transmission lines coupled together over a prescribed electrical length, first applied-energy variable impedance means coupled to a first terminal to one end of the coupled length of said first line, second applied-energy variable impedance means coupled to a second terminal at the other end of the coupled length of said first line, signal means coupled to said first line substantially in the center of its coupled length, means completing a current loop for idler current through said coupled length and both of said variable impedance means, said second line having an input terminal for pump frequency energy at one end of the coupled length, and means at the other end of the coupled length of said second line to adjust a standing wave of pump voltage to apply pump energy to said variable impedance means with substantially equal amplitudes but substantially 180* out of phase.
 2. An amplifier according to claim 1 in which said electrical length is adjusted so that the idler impedance is substantially zero.
 3. An amplifier according to claim 1 in which said variable impedance means are varactors having one pair of like electrodes connected respectively to said first aNd second terminals and the remaining pair of like electrodes connected to a common ground.
 4. An amplifier according to claim 3 in which said adjusting means for said second line is an extension of said second line for a prescribed electrical length beyond said coupled section and terminated in said common ground.
 5. An amplifier according to claim 1 in which said lines are strip conductors in a parallel-plate system.
 6. An amplifier according to claim 3 in which said lines are strip conductors in a parallel plate system, and said common ground is a ground plane of said system.
 7. A balanced parametric amplifier system comprising first and second amplifiers each according to claim 1, hybrid junction means having first, second, third and fourth terminals and the property that a signal introduced via said first terminal is transmitted to said second and third terminals and similar signals introduced at said second and third terminals combine to appear at said fourth terminal, the signal means of said first amplifier being coupled to said second terminal, and the signal means of said second amplifier being coupled to said third terminal.
 8. A balanced amplifier system according to claim 7 in which the second transmission lines of said amplifiers are successive segments of a single transmission line for supporting a single pump voltage standing wave for both amplifiers. 